Refer to FIG. 1. The use of telephone service has dramatically increased as a result of the popularity of the Internet. In addition to a single telephone line for voice conversation, it is increasingly common to find homes with multiple phone lines 135, so that the second line can be used for business or for Internet access.
Wire line residential phone service essentially means connecting a twisted pair of wires 110 originating in the central office of the telephone company to a physical wired circuit, connected to a number of wired phones in the residence 115. These twisted pairs are packaged in bundles of up to several thousand wires, attached to a switch through a wiring frame in the central office and these large bundles are then attached from telephone pole 120 to telephone pole through the neighborhoods. Outside a given residence the particular pair of wires that provide service to that residence is exited from the bundle and brought to the house, where it is attached to the in-house wiring. Once the twisted pair is attached to the in-house wiring, it may be connected to a traditional, wired telephone 125, as is manufactured by Southwestern Bell, GE or Sony.
Cordless phones are terminal devices attached to the existing land line (wired) networks of today. Two devices comprise a cordless phone 130: a base unit and a handset. The base unit connects directly to one or two wired lines of the existing network and extends them by radio to the handset. The cordless phone provides total transparency, viz: the land line network does not know that it is terminated in a cordless phone rather than a traditional wired telephone set. The base unit's main functions are to provide a full-duplex audio channel between the land line and the handset, and an interface between the wired network signaling and appropriate devices in the handset such as the switch hook, the bell (alerting device), and the dial pad. Various methods are used in cordless phones to provide security, meaning protection against unauthorized use of the land line channels, and privacy, meaning protection from eavesdropping. Cordless phones are typically sold in base-handset pairs which can be set to one of several code-patterns by the consumer, usually by means of a multi-contact switch bank. The radio-frequency sections of cordless phones are low-power and with the exception of high-end units which use spread-spectrum frequency-hopping techniques as a security means, they are not frequency-agile, meaning they do not change frequency during a call. In particular, cordless phones do not use frequency agility as a means of improving the switching functions or services of the networks to which they are connected.
Cellular telephone systems, while cordless, are substantially different from cordless telephone sets. Cellular telephone handsets are both frequency-mobile and power-mobile, and are constantly supervised by the cell controller. They use many more frequencies than cordless telephones. The fundamental feature of cellular systems is to provide mobility of the handsets over wide areas, even hundreds of miles. It is not possible to provide sufficient RF power to cover wide areas, and there are insufficient assigned frequencies to serve the number of users on a frequency-per-user basis. As a result, cellular telephony divides all geography into relatively small “cells”, each with a central antenna 140, using a subset of all frequencies, allowing low-power communications with handsets 145, inside the cell boundary. Each cell adjacent to a given cell will use a different subset of frequencies (146, 147), and cells a short distance away can reuse the same frequencies because of the low RF power used in the cells. The control system for cellular telephone systems is extremely complex. Each cell controller continually monitors the signal strength of all handsets in its own cell and in adjacent cells, so when a handset moves into the boundary between two cells, both cell controllers know where the handset is and in what direction it is moving. At the appropriate moment a “hand-off” occurs during which the cell controllers instruct the handset to change to a frequency that is used in the cell it is entering. At the same time the land line connection is changed from the old cell to the new cell, providing continuity for the voice connection.
To provide wireless data access in well trafficked areas such as hotels and airports, firms such as MobileStar (http://www.mobilestar.com) provide publicly accessible wireless LANs. These allow subscribers, equipped with the appropriate passwords, hardware and software for their laptops, to communicate through wireless LAN techniques, and through a gateway and router to their corporate LANs and the Internet. The wireless access point in the airport or hotel is generally provisioned with a broadband (TI or above) wired channel to the network. These facilities are shared rather than dedicated, with the routers functioning to transfer packets to their appropriate destinations.